Process for purifying impure solid-phase kainite



ride, such as are present as impurities in commercially availablelangbeinite and 60% muriate of potash,-seriously reduce the overallrecoveries when practicing the processes heretofore known, .It has beenfound in prac tice that actual recoveries of the order of between about50 65% and about 70% of the K values of the raw materials 'are about ashigh as can be expected by following the processes heretofore practiced.

U. S. Patent 2,684,285 discloses a process which is an improvement overthe process of U. S. Patent 2,295,- 257. The former patent concerns aprocess whereby the potassium sulfate mother liquor obtained, followinga reaction between langbeinite and aqueous potassium chlorideto producepotassium sulfate and the removal of potassium sulfate from the reactionmixture, is concentrated and evaporated to produce certain mixed salts,

overall process is more efficient than the process of U, S.

Patent 2,295,257. I

Heretofore, the liquor of mixed salts has been discardedas waste ortreated to recover the magnesium values therefrom. The potash values, ifrecovered at all, were recovered as low grade These mixed salts areremaining following the removal tween about 36% and about 40%, byweight.

Unlted States Patent 0 "ice i p Patented Dec. 2, 1958 potassium salts,such as kainite. In accordance with the instant invention, the liquorremainingfollowing the re- 2,862,788 moval of the mixed salts, whichliquor will be termed potassium sulfate rejectjliquor, is treated in amanner PROCESS FOR URE SOLID'PHASE 5 to permit the recovery of magnesiumvalues therefrom, l but is also treated to recover a major proportion ofWilliam N. Stanley, Jr., and William B. Dancy, Carlsbad, the potassiumvalues therefrom in the form of high ll. Mex., assignors toInternational Minerals & Chemgrade potassium salts, such as leonite. Inaccordance Kai Corporation, a e p ef Y0!k with a specific embodiment ofthe instant invention, be-

Applicafion May 3, 1955, Serial N6 505,717 0 tween about 60% andaboutt70% of the potassium values contained in potassium sulfate re ecthquor are recovered, 4 Claims. (Cl. 23-38) as potassium sulfate.

-' It is an object of the present invention to increase the overallrecovery of potash values from langbeinite. The present inventionrelates to a process for the treat-' It is another object of thisinvention to recover the ment of liquors to recover potassium valuestherefrom potassium values from kainite containing substantial and, moreparticularly, to a process for recovering poamounts of sodium chloride.tassium and magnesium values from potassium sulfate It is a furtherobject of this invention to provide a re ect liquor. I 7 process forrecovering potash values from potassium sul- In the past, processes havebeen developed involving fate reject liquor. the production of potassiumsulfate over and above the In accordance with the instant invention,kainite conquantities naturally present in langbeinite taining asubstantial quantity of sodium chloride as an impurity 'is treated withwater in a manner to remove (K2804 ZIYIgSOQ substantially all of thesodium chloride from the solid y reactlng an aqueous solutlon or slurryof potassium kainite without altering or dissolving any substantialchloride Substantially free from Sodium chloride with amounts of thekainite. .The kainite can then be utilized leonite and/or schoenitehaving the formulate, respectiveas l ad t h lt or it may be converted toa y 2 4' 4' 2 and 2 4' 4 z higher grade potash salt in accordance withone or more p e potassmm sulfate and a potasswm-containing specificembodiments of this invention. The invention is mother liquor. Theleonite and schoenite are produced i d t by treating kainite which maycontain up y Ieaeting lahgheihite ehbstantiaiiy free of sodium chioi toabout 25% sodium chloride, by weight, with about 1 i wlth the methel' qSeparated from the p part of water for each 3 to 4 parts ofkainite-sodium chlo l Slum Shifaie efystais- In this manner a Portion ofthe ride mixture, for a period of less than about 2 minutes, Potassium}Content of the high p t n preferably for less than about 1 minute atatemperature mother ilqllef is recovered y the Production of the of lessthan about C., preferably at a temperature Solid Salts, leonite andschoenite, which can e Used in of less than about 30. C. Following thetreatment, the the Iedeiio11 p with P a m chloride to Produce liquidphase containing dissolved sodium chloride is" Potassium suifate- ASpracticed in e Past, these P separated fromthe solid kainite. Thetreatmentof'the 6886s h v necessarily involved the use of reactantswhich kainite-sodium chloride mixture with water results in aresubstantially free ofsodium chloride; but it is neces-' the removal f atleast about 75% f h di Y fOiiew a'cempiieated System for handling ride.The purified kainite can be used directly as a intermediate seiifis andliquors as Outlined in Processes, low, grade potash for fertilizerpurposes .or may be treat- Such as these dlsciosed y S; Patent 2,295,25710' ed to recover the potassium values in the form of a Butt et al. Inaddition, concentrations of sodium chlohigher grade hl i In accordancewitha specific embodiment of this invention, potassium values in,potassium sulfate reject liquor may be recovered in the form ofpotassium sulfate. The potassium sulfate reject liquor which containsessentially sulfate, chloride, magnesium and po-' tassium ions isreacted. with carnallite (KCl M gCl 6H O suspended in an aqueous mediumsaturated with respect tomagnesium chloride, the reaction taking'placeat a temperature between about C. and about C. When the reaction issubstantially complete, kainite solids comprising kainite salts whichare formed during the reaction are separated from the mother liquor.

The mother liquor from which the kainite salts have been removedcontains substantial quantities of magnesium chloride. 'Thfis motherliquor is evaporated to a point near saturation with respect tobischofite,

(MgCl -6H O) that is, to a magnesium -chloride.concentration of be- 7Evap: oration is usually carried out at a temperature above, about 60C., preferably at a temperature between about C. and about C. Theresulting mixture is then cooled and thickened, preferably at' atemperature 1 'of about 90 C., which is the optimum temperature for thisthickening step. However, temperatures below about 90 C. may also beemployed for the thickening step. If the evaporation is carried out at atemperature above about 90 C., the concentrated mixture is cooled andthickened at a temperature below about 90 C. If the evaporation iscarried out at a temperature below about 90 C., the slurry is thickenedat the evaporating temperature without additional cooling. The underflowfrom the thickener containing carnallite is recycled to the potassiumsulfate reject liquor reaction.

It is important that the potassium sulfate reject liquor prior to itsreaction wih carnallite be adjusted with, for example, an alkalinecompound such as sodium hydroxide, to a pH-of between about 5.5 andabout 6.5, preferably to a pH of about 6. has a pH substantially belowabout 6, for example, a pH of about 4 or less, considerable corrosion ofequipment occurs and equally, if not more important, the kainite saltsformed as a result of the reaction between the.

carnallite slurry and a highly acidic reject liquor are very difiicultto filter. If, however, the potassium sulfate reject liquor is adjusted.to a pH between about 5.5 and about 6.5, the kainite salts formed arevery easily filterable.

The kainite formed by the reaction between carnallite and potassiumsulfate reject liquor, upon separation from the mother liquor, isfiltered to remove any excess water which may be present. The kainitecontains substantial amounts of sodium chloride and the concentration ofthe sodium chloride will usually range from between about 5% to about20% or more based on the total solids. Ordinarily, there Will be betweenabout and about sodium chloride present based on the weight of thesolids.

According to one embodiment, the kainite containing sodium chloride asan impurity is admixed With water in an amount of about 1 part water toabout 3 parts of solids. The resulting slurry is agitated for less thanabout 1 minute at room temperature. The solids are then separated fromthe liquid phase by any convenient means, for example, by filtration.About 70% of the magnesium values in the kainite-sodium chloride mixtureand about 80% of the potassium values are recovered by this procedurewhile removing at least about 75% of the contaminating sodium chloride.

The kainite from which the sodium chloride has been removed can beutilized directly as a low grade potash salt, but preferably it isrecycled directly to the reaction between langbeinite and aqueouspotassium chloride solution to recover the potash values in the kainiteas potassium sulfate. However, the mixed salts hereinabove mentioned arealso recycled to this reaction station. The separate introduction of themixed salts and kainite increases substantially the difficulty ofmaintaining the overall process within its prescribed reactionconditions. It is preferred that the kainite produced from thekainitepurifying reaction be uniformly admixed with the mixed saltsprior to addition to the langbeinite-potassium chlo ride reaction. Byoperating in this manner, there are no additional variables to becontrolled and the problem of maintaining the essential reactionconditions throughout the overall process is not increased.

The potassium sulfate reject liquors utilized in this invention areillustrated by the reject liquors produced in processes such as aredescribed and claimed in U. S. Patent 2,295,257 to Butt et al., and U.S. Patent 2,684,285 to Dancy. A typical potassium sulfate reject liquorsuitable for the practice of the instant invention contains betweenabout 5.3% and about 6.7%, by weight, of potassium chloride, betweenabout 1.8% and about 3.3%, by weight, of sodium chloride, between about6.2% and about 7.5%, by weight, of magnesium sulfate, between about15.5% and about 18.3%, by weight, of magnesium chloride, and betweenabout 66.0% and about 68%, by weight, of water.

In the kainite formation step sufficient carnallite slurry,

If thepotassium sulfate reject liquor the liquid phase of which issubstantially saturated with magnesium chloride, is added to thepotassium sulfate reject liquor so that the resulting liquor will benearly saturated with respect to carnallite, for example, kainite isobtained by mixing between about 1.15 parts and about 1.35 parts, byweight, of potassium sulfate reject liquor per part of carnalliteslurry. Kainite is formed in the above described slurry at a temperaturebetween about 10 C. and about C. Although kainite is formed in theslurry throughout the entire temperature range mentioned, the rate offormation of kainite is sufficiently rapid to be commercially feasibleonly at temperatures above about 60 C. The kainite salts which areseparated from the solution have a K 0 content of about 22% andmagnesium oxide content of about 15%. The kainite-forming reaction iscarried out until the formation of kainite is substantially complete.This usually requires between about 2 hours and about 4 hours. Thekainite salts produced by the reaction between carnallite and potassiumsulfate reject liquor have a typical analysis after washing and dryingas follows:

Percent by weight Potassium chloride 34.97 Magnesium sulfate 44.67Sodium chloride 19.77

About 93% of the K 0 values in the potassium sulfate reject liquor arefound in the kainite salts.

In another embodiment of this invention, kainite which has been treatedto remove the sodium chloride contaminant as above described is reactedwith potassium sulfate reject liquor, whereby the kainite is convertedto leonite. The proportions of kainite and potassium sulfate rejectliquor are regulated to produce a reaction mixture having a magnesiumchloride concentration below that at which carnallite will precipitate,that is, the magnesium concentration in the reaction mixture ismaintained below about 6.8%, by weight, and preferably as low aspossible. The magnesium concentration is conveniently regulated tobetween about 6.2% and about 6.4%, by weight. The magnesiumconcentration can be reduced by increasing the ratio of potassiumsulfate reject liquor to kainite in the reaction mixture. The reactionmixture is agitated at a temperature between about room temperature andabout 50 C., preferably between about 30 C. and about 35 C., untilsubstantially all of the kainite is converted to leonite. Followingcompletion of the reaction, the reaction product mixture is filtered toremove the leonite solids, and the filtrate obtained, which comprises amagnesium chloride solution, is suitable for separate processing torecover the magnesium values therefrom. The leonite recovered may beutilized directly as a high grade potash fertilizer component, butpreferably it is reacted with langbeinite and an aqueous potassiumchloride solution to produce potassium sulfate. The leonite may be addeddirectly to the reaction vessel, wherein langbeinite is reacted withaqueous potassium chloride solution, but preferably it is admixed withthe mixed salts, and the admixture is recycled to thelangeinite-potassium chloride reaction vessel. By operating in thismanner, rather than by adding the leonite separately to the langbeinitereaction vessel, the number of variable reactants entering thelangbeinite reaction vessel is maintained at a minimum, making it lessdifficult to control the essential reaction conditions in the overallrecovery process.

For a more complete understanding of the instant process reference maybe had to the figure which is a flow sheet of a preferred embodiment ofthe instant process.

An aqueous solution of potassium chloride, for example, 60% muriate ofpotash solution 4 is allowed to enter reaction tank 3 by line 5. Water 6enters the reaction tank byline 7 and langbeinite 1 enters the reactionby line 2. The mixture is agitated and allowed to react at about 45 C.for a period of time sufiicient to allow the reaction to reachequilibrium. Thereafter the reaction product mixture is transferred tofilter 9 by line 8.

The solid potassium sulfate productis removed from the filter 9 by line10 and sent to dryer and storage 13 by line 12. The filtrate 15 fromfilter 9 is removed by line 14 and is transferred to evaporator 17 byline 16. A concentrated material from evaporator 17 is conveyed tocrystallizer 19 by line 18. In the evaporator the filtrate 15 iscarefully evaporated to a point just short of the,

crystallization of sodium chloride and/ or magnesium chloride when theliquid is at room temperature. As previously stated, the evaporation ispreferably carried out below the atmospheric boiling point of the motherliquor, for example, by use of reduced pressure.

The concentrated mother liquor is then transferred by line 18 tocrystallizer 19 where his quickly cooled to below 55 'C. The resultantcrystalline mixture is conveyed to thickener 21 by line where the solids23 comprising essentially potassium chloride, kainite and leonite areseparated and removed by line 22 and recycled to reaction tank 3 by line24. The filtrate 26, which is potassium sulfate reject liquor, isremoved from thickener 21 byline 25 and is conveyed to reaction tank 28by line 27. Carnallite slurry 29 is added to reaction tank 28 by line30. The mixture in reaction tank 28 is agitated and allowed to react ata temperature of between about 60 C. and about 85 C. until kainiteformation is substantially complete. Reaction is usually complete inbetween about 2 hours and about 4 hours. The kainite reaction productmixture is then transferred to thickener 32 by line 31. Overflow 34 fromthickener 31 is removed by line 33. This liquid comprises a concentratedmagnesium chloride solution and is suitable for processing for therecovery of magnesium values therefrom. Solids 36 are removed asunderflow from thickener 32 byline 35. These solids are comprisedessentially of liquor is removed and the filter cake 40 is transferredto reaction tank 42 by line 41. Water 44 is added to the reaction tankby line 43. The amount of water added must amount to between about 25%and about based on the weight of the solids mixture which is added toreaction tank 42. The temperature in reaction tank 42 is maintained atless than about 35 C., and preferably less than about 30 C. The slurryin reaction tank 42 is agitated for less than about 2 minutes, andpreferably less than about 1 minute, and is then transferred by line 45to filter 48 where the liquor containing dissolved sodium chloride 47 isremoved by line 46. A sodium chloride solution 47 contains usually atleast about 75% of the sodium chloride present in the solids 40. Kainitefrom filter 48 is recovered by line 49 and can be recycled by lines 61,62 and 63 to thickener 21 where it is uniformly mixed with mixedsolids-salts 23 to be recycled by line 24 to reaction tank 3or it can godirectly to line 24 from line 61 by way of lines 62 and 64.Alternatively, kainite 50 is transferred to reaction tank 53 by line 51where is is admixed with potassium sulfate reject liquor 26, which isadded to the reaction tank 53 by line 52. The reaction mixture inreaction tank 53 is agitated until the reaction reaches equilibrium.Thereafter, the reaction product mixture is transferred to filter 57 byline 54 and potassium chloride containing solution 56 is removed by line55. Leonite 59 from filter 57 is recovered by line 58 and recycled bylines 60, 62 and 63 to thickener 21 where it is uniformly mixed withsolids 23 comprising mixed salts and recycled with these mixed salts byline 24 to reaction tank 3, leonite 59 or may go directly by lines 60,62 and 64 into line 24 and reaction tank 3. In reaction tank 3 thesemixed salts will react with langbeinite and aqueous potassium chloridesolutions to produce potassium sulfate. Between about 70% and about 80%of all of the potassium values in the potassium sulfate reject liquormay be re- This kainite-sodium chloride mix ture 36 is transferred tofilter 38 by line 37 where excess covered in accordance with the instantprocess as potassium sulfate. Also, filtrate 56 and overflow 34, whichare to be processed for the recovery of potassium values and magnesiumvalues, are substantially free of excessive amounts of sodium chloride,the sodium chloride having Table 1 T K Mg Na or so. ago

Potassium sulfate reject liquor 3.40 5. 44 1.12 16. 84 5.19 68.01Carnallite slurry. 90 6.01 8.94 1; 29 32.20 1.78 49. 78 Crude kainite---11.47 8.55 3. 82 18.40 30. 73 27.03 Washed kainite 13.05 8:55 1.17 13.8033.19 30.23 Filtrate 3. 81 4. 04 3.60 11252 11.03 65.00

'The resulting mixture was agitated at a temperature of about 65 C.until the sulfate concentration of the liquor had been reduced to belowabout 2%. The kainite salts which crystallized wereseparated from theliquor. Fifty parts of crude kainite filter cake were agitated with 17.5parts of water for 1 minute at 28 C. The slurry Was immediatelyfiltered. About 75% of the sodium chloride present in the crude kainitefilter cake was dissolved in the; 9

water and removed by the filtration and about 70% of the magnesiumvalues in the crude'kainitefilter cake was re-j covered as washedkainite. The washed kainite also contained about of the potassium valuesin the crude kainite filter cake. The washed kainite was admixed withmixed salts and the mixture added to langbeinite and aqueous potassiumchloride solution in sufiicient amounts to produce a reaction mixturehaving an analysis as shown in Table 2. The reaction mixture wasagitated for about 4 hours at a temperature of about 45 C. The reactionproduced solid potassium sulfate which was removed by filtration.

- EXAMPLE -II A washed kainite from which contaminating sodium chloridehas been removed as in Example I was admixed with sufficient potassiumreject liquor having a composition as indicated in Table 1 to produce areaction mixture having a magnesium concentration of about 6.3%, byweight. The reaction mixture was agitated at a temperature of about 35C. until the reaction reached equilibrium. Leonite was formed during thereaction and was separated from the reaction mixture by filtration. Theleonite was then admixed with mixed salts and the admixture reacted withlangbeinite and potassium chlo ride solution to produce potassiumsulfate. The mixed salts containing the added leonite, langbeinite andaqueous potassium chloride solution were added to the reaction tank insufiicient amount to produce a reaction mixture having an analysis asindicated in Table 2.'

potassium sulfate reject liquor hav- 7 Potassium sulfate which wasproduced by the reaction was separated from the reaction product mixtureby filtration and dried. By operating inaccordance with this example,about 75% of the potassium values in potassium sulfate reject liquor wasrecovered as solid phase potassium sulfate.

Having thus fully described and illustrated the character of the instantinvention, what is desired to be secured by Letters Patent is: p I

1. A process for purifying impure solid-phase kainite containingsolid-phase sodium chloride as an impurity in a proportion between aboutand about 25% by weight, based on total solids, which comprisesslurrying said impure kainite with between about 25 and about 35% byweight of. water, based on total solids, at a temperature of less than.about 35 C. for a contact time, less than about 2 minutes, sufficient toselectively dissolve at least about 75 of the solid-phase sodiumchloride contained in said impure kainite, and separating solid,purified kainite from the liquid phase.

2. A method as in claim 1 wherein said impure kainite is slurried withwater for a contact time of about 1 minute.

3. In a process for recovering potassium values from potassium sulfatereject liquor which comprises reacting a potassium sulfate reject liquorcontaining sulfate, chloride, magnesium, potassium, and sodium ions witha suspension of carnallite in an aqueous medium substantially saturatedwith respect to magnesium chloride at a temperature between about 60 and85 C., separating impure solid-phase kainite from the resulting mixtureupon substantial completion of the reaction, said kainite containingbetween about 5 and about 25% by weight of solid-phase sodium chlorideas an impurity, based on total solids, and washing said impure kainite,the improved method of washing which comprises slurrying said'impurekainite with between about 25 and about 35 by weight of water, based ontotal solids, at .a temperature of less than about 35 C. for a contacttime, less than about 2 minutes,

suflicient to selectively dissolve at least about 75% of the solid-phasesodium chloride contained in said impure kainite, and separating solid,purified kainite from the liquid phase.

4. In a process for recovering potassium values from kainite containingbetween about 5 and about 25% by weight of sodium chloride, based ontotal solids, as an impurity, wherein said kainite is admixed withwater, potassium chloride, and langbeinite, the mixture is agitated at atemperature-between about 15 and about C. for a period of about 1 toabout 4 hours, andthe resulting crystals of potassium sulfate areseparated from the reaction product mixture, the improvement whichcomprises pretreating said kainite in solid form by slurrying withbetween about 25 and about 35% by weight of water, based on totalsolids, ata temperature of less than about 35 C. for a contact time,less than about 2 minutes, suflicient to selectively dissolve at leastabout of the solid-phase sodium chloride contained in said kainite, andseparating solid kainite, depleted of sodium chloride, from the liquidphase, whereby sodium chloride contamination inthe subsequent operationsis substantially reduced.

References Cited-in the file of this patent UNITED STATES PATENTS1,589,519 Dolbear June 22, 1926 1,794,553 Schoch Mar. 3, 1931 2,684,285Dancy July 20, 1954 2,687,339 Dancy et a1 Aug. 24, 1954 OTHER REFERENCESMellor: Comprehensive Treatise on Inorganic and Theoretical Chemistry,vol. 4, page 340. Longmans, Green and Co., N. Y., 1923.

Seidell: Solubilities of Inorganic and Organic Compounds, vol. 1, pages387, 396, 556 and 640. D. Van Nostrand Co., N. Y., 1919.

1. A PROCESS FOR PURIFYING IMPURE SOLID-PHASE KAINITE CONTAININGSOLID-PHASE SODIUM CHLORIDE AS AN IMPURITY IN A PROPORTION BETWEEN ABOUT5 AND ABOUT 25% BY WEIGHT, BASED ON TOTAL SOLIDS, WHICH COMPRISESSLURRYING SAID IMPURE KAINITE WITH BETWEEN ABOUT 25 AND ABOUT 35% BYWEIGHT OF WATER, BASED ON TOTAL SOLIDS, AT A TEMPERATURE OF LESS THANABOUT 35*C. FOR A CONTACT TIME, LESS THAN ABOUT 2 MINUTES, SUFFICIENT TOSELECTIVELY DISSOLVE AT